Jet engine automatic thrust control



Feb. 27,l 1962 A. M. PRENTlss 3,022,628

JET ENGINE AUTOMATIC THRUST CONTROL Original Filed May 26, 1948 5Sheets-Sheet 1 INVENTOR Feb. 27, 1962 A. M. PRENTlss 3,022,628

JET ENGINE AUTOMATIC THRUST CONTROL Original Filed May 26, 1948 5Sheets-Sheet 2 "iif- 3 54144545 '2567/92 5Fl? .5A/Vif A5 [N6/AlfxNvEN'roR Feb. 27, 1962 A. M. PRENTISS JET ENGINE AUTOMATIC THRUsTCONTROL 5 Sheets-Sheet 3 Original Filed May 26, 1948 Enf., kh,

Feb. 27, 1962 A. M. PRENTlss JET ENGINE AUTOMATIC THRUST CONTROL 5Sheets-Sheet 4 MEE VN hw Feb. 27, 1962 A M, PREN-rlss 3,022,528

JET ENGINE AUTOMATIC THRUST CONTROL Original Filed May 26, 1948 5Sheets-Sheet 5 hamaca TM" QQ" I. i //3 l g l :mnil l //2 i g `\l qm ,L xmj,

f ./Q [NGV/VE /Nzfr 2 3 al? 00H57 7 INVENTOR ATTORNEY United StatesPatent 3,22,628 Patented Fein. 27, 1962 ffice JET ENGM AUTOMATC THRUSTCONTROL Augustin M. Prentiss, Hartford, Conn., assigner, by

niesne assignments, to Chandler-Evans Corporation,

West Hartford, Conn., a corporation of Delaware Continuation ofabandoned application Ser. No. 29,384,

tiled May 26, 1948. This application Aug. 2a, 1954,

Ser. No. 4S,829

12 Claims. (Cl. Gti-35.6)

This application is a continuation of application Ser. No. 29,384, filedMay 26, 1948, now abandoned.

This invention pertains to automatic controls for jet engines and moreparticularly has reference to controls for regulating and equalizing thethrusts from the several jet engines of multi-engine aircraft. Whilethis invention is primarily applicable to plain (ram) jet and turbojetengines without Propellers, it also applies to turbojet engines withpropeller (prop-jet), where a substantial part of the propelling powerof the engine is exerted through the jet effect of its exhaust gases.Unless otherwise qualified, it will be understood that the term jetengines, as used in this application, includes all of these types ofengine.

in the operation of high speed aircraft, propelled by jet engines, it isessential not only that the thrust of each engine be at all times underthe control of the pilot, but also in multi-engine aircraft the thrustsfrom the several engines be equalized and balanced, in order that no yawmoment be developed tending to make the airplane go off course.

In multiple, jet-engined aircraft, moving at speeds approaching orperhaps exceeding sonic velocity, small differences in thrust betweendifferent engines may cause a material yaw moment to prevail, and incase of a substantial loss of thrust by any engine, the yaw moment, ifnot rapidly corrected, may result in serious difficulties.

Heretofore, the performance of an aircraft turbojet engine withpropeller (prop-jet) has generally been controlled by regulating thespeed (rpm.) of the engine and/or the pitch of the propeller, so as tomaintain a constant speed and/or thrust of the propeller for any givensetting of the pilots control lever, and in the turbojet enginedaircraft, without propeller, the performance of the engine has beencontrolled by regulating the speed of the gas turbine which drives itsair compressor, so as to maintain a constant speed of the engine withany given setting of the pilots control lever. In multi-engine aircraft,with both turbo-jet and prop-jet engines, the aerodynamic balance of theairplane has been controlled by synchronizing the speed (rpm.) of theseveral engines, usually based on the speed of one of the enginesselected as a master engine.

With prop-jet engines at the higher speeds, when a considerable part ofthe thrust developed by the engines is due to the jet effect, and withturbo-jet and ram-jet engines at all speeds, experience has shown thatthe aerodynamic balance of a multiple engine airplane cannot besatisfactorily controlled by synchronizing only the speeds of theseveral engines, because for the same engine speed (rpm.) the thrust ofany engine may vary as much as to 15%, depending upon the operatingcharacteristics and condition of the particular engine. Accordingly, inorder that a multi-engine airplane may y a straight course, it isnecessary to balance the thrusts of the several engines and to maintainthis balance at all times, preferably without manual manipulation by thepilot.

Experience has also shown that turbojet and ram-jet engines mayencounter difticulties from excessive engine speeds and/ ortemperatures, and it has been customary heretofore to provide eachengine with a device responsive to engine speed (rpm.) and/or (tailpipe) temperature which will override the automatic control and limitthe speed of the engine to a maximum safe rpm. whenever greater speedsand/or temperatures are developed in the engine. In regulating andequalizing the thrusts of the several jet engines of multi-engineaircraft, it is also desirable to provide means for preventing theoverspeeding and/or overheating of any engine without disturbing thebalance of the group.

In a multi-engine aircraft, it is also desirable that the pilot be ableto normally control all the engines from a single manual control lever,but each engine should be capable of operation independently of all theothers, so that in case trouble develops in any one engine, causing itto operate below par, the efficiency of the other engines will not beaffected.

ln a companion application of Milton E. Chandler, Serial No. 23,936,iled April 29, 1948, now Patent No. 2,853,851, and assigned to the sameassignee as this application, there was disclosed a hydraulicallyoperated control system for the jet engines of a multi-engine aircraft,wherein each engine was mounted so as to be movable with reference tothe chassis of its airplane, and the jet thrusts of all the engines wereautomatically regulated and equalized by the movements of each engine,so that the thrusts of all the engines were balanced with each other,and any yaw moment tending to make the aircraft go oit` course waseliminated. In that control system, the operation of a plurality of jetengines was controlled by selecting one engine to' function as a master,and this engine controlled the performance of the other engines of thegroup as slave engines.

Such a control system is open to three objections, which the inventionherein disclosed is designed to overcome. First, movably mounting theengines requires specially designed bearings and structural modicationsin the chassis of the airplane. Secondly, movably mounted engine requirespecial compensating means `for forces due to engine mass, i.e., weightand inertia effects of the engine. Thirdly, the use of one engine of amultiengine aircraft to control the operation of the other enginesnecessarily limits the overall performance of the whole group to that ofthe master engine, and whenever the performance of that engine is belowpar or average performance of the group, there is an unavoidable loss ofpower and eiciency of all the other engines.

The invention herein disclosed is, therefore, in the nature of animprovement over that disclosed in the companion application citedabove.

Accordingly, an object of this invention is to provide means forcontrolling the speed of flight of a jet-engined aircraft by regulatingthe performance of all the engines from a single manual control lever,which is adapted to secure from each engine a desired thrust, whichproduces a desired speed of light, corresponding to the position of saidlever, and means `for automatically equalizing the thrust of each enginewith that of the others.

Another object is to provide means for automatically controlling theoperation of plurality of jet engines of a multi-engine airplane, inresponse to a manual control element of one of the engines selected as amaster control, so that the thrusts from all the engines is equalizedand balanced.

Another object is to provide pneumatically actuated means forautomatically regulating and equalizing the thrusts from a plurality ofjet engines in a multi-engine airplane so that no yaw moment will beproduced tending to make the airplane go oft' course.

Another object of this invention is to provide al control system for agroup of jet engines in a multi-engine aircraft, where each engine isprovided with an identical control, and all these controls are sointer-related that the performance of all the engines can be controlledfrom the single manual control lever, pertaining to any one of theengines, but each engine operates independently of all the others, sothat below par performance of any engine does not laiect the elciency ofthe other engines.

Another object of this invention is to provide means for controlling theoperation of a jet engine by means of the differential pressure producedby the velocities of its air supply and exhaust gases, so as to obtain adesired lthru-st in response to any gulven setting of the pilots controllever, within the limits of safe temperature and/ or speed of theengine.

Still another object is to provide a speed and/or temperature overridecontrol device for each engine of a multi-engine airplane, so that ifthe speed and/or ternperature of any engine should exceed apredetermined safe limit, the override device temporarily takes controlof that engine and reduces its speed and/ or temperature to safeoperating limits, as determined by the setting of the override controldevice.

With lthese and other objects in View which may be incident `to myimprovements, my invention consists in the combination and arrangementof elements hereinafter described and illustrated in the accompanyingdrawings in which:

FIGURE l shows, schematically, one embodiment of my improved controlsystem as applied to an airplane propelled by a plurality of jetengines, wherein only one manual control device is provided forcontrolling all the engines of a multi-engined aircraft.

FIGURE 2 shows, schematically, an alternate arrangement of my improvedcontrol system, wherein an identical manual control device is providedfor each engine, but only one, Ias selected by the pilot, is used at anyone time to control the operation of iall engines of a multienginedaircraft, and all the other manual controls are locked in an inoperativeposition.

FIGURE 3 lis a schematic view, on a larger scale, of engine No. 1 ofFIGURE 1.

FIGURE 4 is a schematic view, on -a larger scale, of engine No. l ofFIGURE 2,

, FIGURE 5 is a schematic view on a larger scale, of the maximumtemperature and speed controls of FIG- URES 1 and 2.

FIGURE 6 is a fragmentary longitudinal section of either the lair intakeduct or tailpipe of the engines of FIGURES l and 2, showing means forvarying the crossseotional areas of these elements.

FIGURE 7 is a schematic view of the mechanism for operating the meansshown in FIGURE 6, either manually from the pilots control lever orautomatically by the regulating systems shown in FIGURES 1 and 2.

FIGURE 8 is a schematic View, partly in section, of the device forregulating the fuel/ air mixture in the engine, by either the flow ofair to the engine, or the discharge of exhaust gases therefrom, when theregulating system shown in FIGURES l and 2 is used for controlling theoperation of the engine by varying the area of the air intake, or thearea of the exhaust gas nozzle, of the engine.

FIGURES 9A and 9B are vertical cross-sectional views, on an enlargedscale, of one of the elements of the regulating vsystems shown inFIGURES 1 and 2, the section Y in FIGURE 9B Vbeing along the line B-B ofFIGURE 9A.

Since the iluid thrust of a jet engine is a function of the mass airowlthrough the engine and since a Pitot tube rnesaures the velocity headof a fluid current, the control of the thrust from a jet engine can bebased upon the Velocity heads, as measured by a Pitot tube, at the airinlet and at the exhaust gas outlet of the engine. The generalrelationship of the several factors involved is as follows.

Let: V=Volume of air (in eu. ft.) passing through engine in tseconds.

4 W=Weight of air (in lbs.) passing through engine in t' seconds.V1=Entering velocity (ft. per sec.) of air=velocity of plane.

v2=Leaving velocity (ft. per sec.) of gases=discharge velocity of jet,relative to plane. i

p1=Tota1 pressure (lbs. per sq. ft.) of entering air. p2=Total pressure(lbs. per sq. ft.) of discharge gases. 'y1=Weight (lbs. per cu. tt.) ofentering air. 72=Weight (lbs. per cu. ft.) of discharge gases.T1=Ternperature (abs. C.) of entering air. T 2=Temperature (abs. C.) ofdischarge gases. F1=Crosssectional area (sq. ft.) of air intake duct.F2=Crosssectional area (sq. ft.) of tail pipe. h1=Head (in feet) ofentering air. 112=Head (in feet) of discharge gases. =Coef. of efliux ofdischarge gases. P=Total thrust, in pounds, of the discharge jet.g=Acceleration due to gravity (32.2 lbs. per sec.2). The mass of airpassing through the engine has its velocity increased from v1 to v2- Toaccelerate W pounds of air from v1 to v2 in t seconds requires a forceP= (acceleration of air) A Pitot tube yat the air inlet and gas outletgive indications Where k=Coef. of llow which varies from 2.00 to 1.00,

depending upon shape of entrance of tube. The coeiiicient g' also variesfrom 2.00 to 1.00, depending upon -shape of engine. By properly shapingentrance to Pitot tubes, k may be made Therefore, Pitot tube readingsindicate:

Substituting these values in Equation 2 We have Where ya, Tl and 11l arethe density, temperature and pressure of the atmospheric air outsideengine, and

Thrust is, therefore, a function of air intake and tail pipe areas, airintake and tail pipe Pitot readings, the coetcient or" tlow, and thedensity of the discharge gases, which last factor is equal to thedensity of atmospheric air, modified by the ratio of atmospherictemperature and pressure to temperature and pressure of the dischargegases.

When K is equal to 1.00, then from Equation Where is greater than 1.00,it has a substantially constant value by which the ratio F1/F2 must bemultiplied, and this somewhat increases the coecient of h1 in Equation6.

Referring to FIGURE 1 of the drawings the reference numeral 1 denotesthe body of a ram-jet engine having the usualV air inlet 2, combustionchamber 3 with burner nozzles 4 and flame holders 5 therein, followed bya tail pipe 6 ending in an exhaust gas outlet 7. If the `engine is aturbojet, the combustion chamber 3 with burner nozzles 4 is locatedfurther toward the tail pipe 6 and is preceded by an air compressor andfollowed by a gas turbine. In either type of engine, the power outputmay be controlled by either varying the fuel supply to the burnernozzles 4, or by varying the air supply rough air inlet 2 to thecombustion chamber 3, or by varying the discharge of exhaust gasesthrough the outlet 7. Since the improved engine control system hereindisclosed is equally applicable to either a ram or turbojet engine,(with or without propeller), the detail construction and arrangement ofthe engine forms no part of my invention.

A Pitot tube 8 facing upstream, is placed near the center of the airinlet 2 and a small air conduit 9 parallels Pitot tube 8, but has itsopen end at right angles to the opening of the Pitot tube and thedirection of air ilow. Another Pitot tube 10 and air conduit 11 aresimilarly Vlocated near the center of the exhaust gas outlet 7. Pitottube 8 and conduit 9 lead into a chamber 12 on opposite sides of adiaphragm 13, which divides chamber 12 into two air-tight compartments.Pitot tube 10 and conduit 11 are similarly arranged with reference to achamber 14 and diaphragm 15. Slidably mounted in chamber 12 is a rod 16,which is attached to diaphragm 13 and biased toward the left by a spring17. A rod 18 and spring 19 are similarly mounted in chamber 14. Theadjacent ends of rods 16 and 18 are bifurcated and pivotally atached toopposite sides of a slotted cylindrical link 20. Slidably mounted in thecylinder of link 20 is a pivot block 21 which is pivotally connected toan arm 22 carried by a rack 23 which is reciprocally mounted in fixedsleeves 24 and 25. A pinion 26 engages rack 23 and is adapted to berotated by a device which varies the cross-sectional area of either theair inlet 2 or the exhaust gas outlet 7, as hereinafter disclosed, sothat the position of the pivot block 21, about which link 29 rocks, isshifted in proportion to the degree of opening of either the air inlet 2or the exhaust gas outlet 7. The Vdevice which varies thecross-sectional area of the exhaust gas outlet may be manually operatedby connecting it to the pilots control lever, or it may be automaticallyoperated by the control system as hereinafter disclosed (see FIGURE 7).

AFrom the arrangement just described, it is clear that diaphragm 13 inchamber 12 is subject to the diierence between the velocity and staticheads at the air inlet 2, land diaphragm in chamber 14 is similarlysubject to the dilerence between the velocity and static heads of theexhaust gases at the outlet 7. The air current entering air inlet 2gives rise to a pressure pa in Pitot tube 8, while the static head atthe same point maintains a lower pressure pb in conduit 9, and thedilerence between these pressures (pa-pb) is a measure of the velocityhead h1 at air inlet 2. Similarly, the exhaust gas current issuing fromoutlet 7 gives rise to a pressure pc in Pitot tube 10 while the statichead at the same point maintains a lower pressure pd in conduit 11, andthe difference between these pressures (pc-pd) is a measure of thevelocity head h2 at outlet 7. Since the pressures pa and pc alwaysexceed the pressures pb and pd respectively, diaphragms 13 and 15 exerta net thrust on rods 16 and 13 to the right in opposition to springs 17and 19. These springs are made very light and are both of the samestrength. Their purpose is merely to steady the movements of thediaphragms 13 and 14 under variations in pressure. Since these springsact in opposite directions on link 2u, they balance each other and theirnet eiect on link 2@ is negligible. Diaphragms 13 and 15 are of the samesize and therefore exert thrusts on rods 16 and 1S respectivelyproportional to the velocity heads h1 and h2.

When pivot 21 is in a position midway between the pivots of rods 16 and18, as shown in FIGURE l these rods act with equal leverage on link 20and hence the net t rust on rod 18 is proportional to h2h1. This is thecondition coinciding with Equation 6a and represents the situation whenthe cross-sectional area F2 of the eX- haust gas outlet 7 is equal tothe area F1 of the air inlet 2. As the area F2 is progressively reduced,by the device mentioned above, while the area F1 remains the same, thedevice which reduces the area F2 also simultaneously moves the pivot 21a proportional distance downward, so as to progressively increase theleverage of link 20 on rod 16, as compared to that of rod 18. Thus, whenpivot 21 is moved down one-half of the distance between its mid-positionas shown in FIGURE 1) and the pivot of rod 18, the leverage of rod 16 onlink 241 is three times that of rod 18, and therefore coincides withEquation 6b when outlet area F2 is equal to one-half of inlet area F1.Similarly, when pivot 21 is moved down twothirds of the distance betweenits mid-position and the pivot of rod 18, the leverage of rod 16 on link26 is live times that of rod 18, and therefore coincides with Equation6c, when outlet area F2 is one-third of F1. Finally, when pivot 21 ismoved down three-fourths of the distance between its mid-position andthe pivot of rod 18, the leverage of rod 16 on link 21 is seven timesthat of rod 1S, and coincides with Equation 6d, when outlet area F2 isone-fourth of F1, which is its minimum opening.

From what has been shown above, it follows that the net thrust to theright on rod 1S is generally proportional to the jet thrust of theexhaust gases of the engine, for varying velocities of air iiow throughthe engine, and for varying opemngs F2 of the exhaust gas outlet fromits full open area (=F1) to one-fourth that area. Also from aninspection of Equation 5, if the net thrust on rod 18 is compensated forvariations in the density y2 of the exhaust gases issuing from outlet 7,this compensated thrust is linearly proportional to the jet thrust ofthe engine and may therefore be used to control the operation of theengine in accordance with its jet thrust. This compensation is effectedby the following device. Rod 18 is pivotally connected through a link 27to the stem 28 of a servo valve 29. Slidably mounted on link 27 is asleeve 30 which is pivoted to an arm 31 integral with a rod 32 which isreciprocally mounted in the xed sleeve 33 and the bottom wall of acyliner 34 which is composed of thermal insulating material.

A thin metal partition wall 35 divides cylinder 34 into an innercylindrical chamber 36 and an outer annular space 37. A sealed bellows3S is fixed tothe top wall of Y the engine is in operation.

chamber 36 and has its movable end attached to rod 32. Bellows 38contains a temperature and pressure responsive fluid whichV is sealedtherein at standard atmospheric temperature, Ts (15 C.) and pressure, ps(14.7 lbs. per sq. inch), at which the iluid has a density 7S. ChamberY36 is connected by a conduit 39 to Pitot tube 10 so that it containsexhaust gases at a pressure p2. Annular space 37 is connected at itsupper end by a conduit 40 composed of thermal insulating material withthe exhaust gas outlet 7, and has at its lower end on the opposite sideavent 41 to the atmosphere. As the pressure p2 in conduit 40 is alwayshigherV than the atmospheric pressure outside the engine, a continuouscurrent of exhaust gases, at their temperature, T2, ows through annularspace 37 and thereby maintains a temperature T2 therein. Partition 35 iscomposed of a thin metal of high thermal conductivity and cylinder 34 ismade of thermal insulating material so that the current of exhaust gasesflowing through space 37 maintains the temperature T2 in chamber 36,while Accordingly, the uid in bellows 38 is subjected to a pressure p2and'temperature T2 at all times that the engine is operating. Thedensity 'y2 of .the exhaust gases in chamber 36 is related to thedensity 'ys in the bellows 38 according to the formula:

so that j n 72 ps XTE And since ('ysTs/ps) is a constant (C) for the uidin bellows 38,'it follows that 72:6' pz/ T 2. As the tempera- Vture ofthe exhaust gases T2 increases the fluid in bellows 38 will expand andmove the lower end of the bellows and rod 32 downward proportionally tothe rise in temperature T2, and vice versa. At the same time, anincrease in the pressure of the exhaust gases p2 will contract thebellows 38 and move the lower end of the bellows and rod 32-upward inproportion to the rise in pressure p2, and vice versa. From theforegoing, it follows that the movement of rod 32 will be in linearproportion to variations in the density y2 of the exhaust gases. Y

As the arm 31 on rod 32 raises or lowers the position of Pitot sleeve30, it proportionally varies the thrust on Vstem-28 of servo valve 29caused by the net thrust of rod 18 on the other end of link 27. Thethrust on stem 28 is therefore proportional to the net thrust on rod 18,modified by variations in the density 'y2 of the exhaust gases, andVsince the net thrust on rod 18 is proportional to the jet thrust of theexhaust gases, the force exerted on servo valve 29 by rod 28 is inlinear proportion to the jet thrust of the engine and may therefore beused to control the operation ofthe engine in accordance with its jetthrust.

Servo valve 29 is of the conventioned spool type, having two cylindricalend portions connected by a center portion of reduced diameter, and isslidably mounted in a cylinder 42 which is connected by conduits 43 and44 to an oil pump 45 driven by an air current motor 91, or by the engine1 (if of the turbojet type). An oil tank 46 is connected by a conduit 47to pump 45 and by a drain pipe 48 to cylinder 42. Another drain pipe 49connects tank 46 to the cylinder 50 of a second servo valve 51 which isalso connected to pump 45 by conduit 44, and to cylinder 42 by conduits52 and 53. A conduit 54 connects cylinder 42 with the cylinder 55 of anhydraulic motor 56, of which the piston 57 is connected by means of arod 58, link 59, lever 60, and link 61 to the regulating arm 62 of avariable delivery fuel pump 63. A spring 64 in cylinder 55 biases piston57 downwardly in opposition to the iluid pressure in the lower end ofcylinder 55. Lever 60Vis mounted on a pivot 65, so that when an increasein tiuid pressure in cylinder 55 pushes piston 57 lll?, arm 62 on pump63 is moved down in a counter-clockwise direction which increases thefuel delivery of the pump through a conduit 66 to burner nozzles 4 incombustion chamber` 3, and vice versa.

Pivot 65 oflever 60Y is movable by the reciprocation of rod 74 in fixedsleeve 75, in response to the temperature and speed of engine 1, rod 74being pivotally connectexi through a floating lever 76 to a maximumtemperature override control device 78.

As shown in FIGURE 5, temperature control device 77 comprises a cylinder91 having a stem 92 connected 'at its upper end by a link 93 with theright end of floating lever 76, and attached at its lower end by a screwto one endof a larger cylinder V96, mounted in the wall of tail pipe 6of the engine so as to project into the stream of exhaust gases flowingthrough said tail pipe. Cylinders 91 and 96 are made of diiferentmetals, having widely dilferent coefficients ofy thermal expansion, sothat when heated by the exhaust gases in tail pipe 6, cylinder 91expands at a much greater rate than cylinder 96. Hence, as thetemperature of the exhaust gases rises in tail pipe 6, cylinder 91,expanding at a greater rate than cylinder 96, raises stem 92, link 93and the right end of lever 76, thus reducing the fuel now from pump 63to the engine, until the decreasing speed of the engine restores thetemperature in tail pipe 6 to the selected maximum safe value. Y

Speed control device 78 comprises Va cam 97, xed to shaft 98 on which isalso xed a gear pinion 99 that meshes with a toothed rack 100, carriedby a sleeve 101, which is slidably mounted on a shaft 102 of fly-ballspeed Vgovernor 103. Shaft 102 is driven by the engine and lcarries afixed collar 104 to which are pivotally attached weighted arms 105connected by links 106 to sleeve 101. A tension spring 107 connected toarms 105 opposes the centrifugal force tending to open arms 105 uponrotation by shaft 102. As the speed of rotation of the engine increases,arms 105 open and lower sleeve 101 which rotates pinion 99 and cam 97 ina counter-clockwise direction. This raises the left end of oating lever761which bears against cam 99, and reduces the fuel ow from pump 63 tothe engine until the decreasing speed of the engine reaches its selectedmaximum safe value.

By virtue of this arrangement, whenever the temperature in tail pipe 6of engine 1 exceeds a'selected maximum safe temperature, overridecontrol device 77 raises the right end of lever 76, and thereby thepivot 65 of lever 60, which reduces the rate of delvery of fuel by pump63 to the engine. vThis causes the engine to reduce its speed and lowersthe temperature in tail pipe 6, until said temperature is within themaximum safe limit.

Similarly, whenever the speed of engine 1 exceeds a selected maximumsafe r.p.m., override control device 78 raises the left end of lever 76,and thereby the pivot 65 of lever 60, which reduces the rate of fueldelivery of pump 63 to the engine. This causes the engine to reduce itsspeed until its r.p.m. is within the maximum safe limit.

Mounted in cylinder 42 to the left of servo valve 29 is a piston 67which is biased to the left by an interposed spring 68. The left end ofcylinder 42 is connected through conduits 53and 69 to the right end ofcylinder 50. Accordingly, any movement of servo valve 29 to the lefttransmits a thrust in the same direction through spring 68 to piston 67which is resisted by the pressure of the oil in the left end of cylinder42. This presureis transmitted through conduits 53, 52 and 69 to thespace lbetween the ends of servo valve 5l and to the right end ofcylinder V50. The thrust thus exerted on servo valve 51 tends to move itto the left in opposition to a force `exerted by a spring 70 through alever 71 which is mounted on a `fixed pivot 73 and connected to a rod 72attached to the left end of servo valve 51. The force of spring 70 isvaried by a manual control lever 80 through a link 81 and lever 82.Levers 80 and 82 are mounted on fixed pivots 83 and 84 respectively, andlever 80 engages with pilots control lever.

a quadrant 85 which is graduated to indicate the jet thrust developed bythe engine and holds the control lever S9 in a ixed position as set bythe pilot.

Conduit 69 from engine No. 1 connects through branch conduits 86 withservo valve cylinders 42 of engines Nos. 2, 3 and 4. Each branch 86corresponds to conduit 53 of engine No. 1 and each has a cut-oit valve87 which permits any of the engines to be cut out of the common controlsystem, without affecting the operation of the other engines o thegroup, in case of trouble developing in any particular engine.

Servo valve 51 and its asociated mechanism are common to the whole groupof engines and constitute the only master control for the group. InFIGURE l this master control is shown as located and associated withengine No. 1, but it does not pertain to engine No. 1, any more than toall the other engines. 1n tact, it is preferably located centrally inthe airplane, close to the When the master control is located in aposition removed from all the engines, the control system for eachengine is as shown in FIGURE 1 for engine No. 2.

The alternate arrangement of my control system shown in FIGURE 2 isessentially the'same as that shown in FIG- URE 1 (with the samereference numerals denoting like parts) except as follows:

(l) An independent manual control is provided for (2) The manualcontrols not selected to control the vgroup are rendered inoperative bylocking the lower end of each lever 71 by means of a cam latch SS whichis rotated manually 90 in a counter-clockwise direction (see FG. 4).

(3) Servo valves 29 and 51 (of FIGURE 1) are mounted in a commoncylinder 42'--50, with piston 67 interposed between them, and a bridgeconduit 89 replacing conduits 52 and 53 of FIGURE 1. Also, conduit 69 iseliminated and branch conduits 86 are connected directly to conduit 89.

The vent 90 to atmosphere prevents compression of the air in spacebetween servo valve 29 and piston 67 (in FIGURES 1 and 2).

A simple mechanism for varying the area F1 of air inlet 2 (when appliedthereto), or for varying the area F2 of exhaust gas outlet 7 (whenapplied thereto), is illustrated in FIGURES 6 and 7, wherein thereference nurn- `eral 110 denotes either the air inlet duct 2 or thetailpipe 6 through which the air enters the engine or the exhaust gasesescape therefrom. The full line arrows in FIG- URE 6 indicate thedirection of the entering air when 'element 110 is an air inlet; aud thedotted line arrows indicate the direction of iiow of the exhaust gases,when 110 is the tailpipe. Member 11() has an inwardly tapered portion111 at its open end in which is concentrically located a similarlytapered choke pipe 112, slidably mounted on a iixed cylindrical sleeve113, which is located concentrically in the inner cylindrical portion ofmember 11G. The cylindrical portion of choke pipe 112 telescopes oversleeve 113 with a free-running but substantially closed tit thereon, andis provided on its outer surface with a toothed rack 114 which engages apinion 115 iixedly mounted on a shaft 116 which extends through the wallof member 110. Outside member 110, shaft 116 has also fixed thereon asecond pinion 117 (FIGURE 7) which engages a toothed rack 11S, integralwith a rod 119 which may be connected by a bell crank lever 126 to link61 (FIGURE 1), in lieu of arm 62, which is disconnected, so that thepump 63 is no longer controlled by the control apparatus shown inFIGURES 1 or 2. In this case, shafts 116 and 26 are interconnected asjust indicated, and pump 63 is controlled by a bellows 121 which may beconnected to either the air inlet 2, or exhaust gas loutlet 7, asdesired (see FIGURE 8).

Alternatively, rack 118 may be connected by a link 122 to the lower endof manual control lever 89 (FIG- URE 1) when it is desired to have thearea F1 of air inlet 2, or area F2 of exhaust gas outlet 7, manuallyadjusted by the pilot. In this case, shaft 116 (FIGURE 6) is connectedto the shaft of pinion 26 (FIGURE 1) by suitable meshing gears (notshown), so that rotation of the former will cause corresponding rotationof the latter in a desired ratio.

In either case, when bell crank lever 121) is rotated counterclockwise,it pushes rod 119 and rack 11S to the left. This rotates pinions 117 and115 in a counterclockwise direction which moves choke pipe 112 to theright. As choke pipe 112 moves to the right, it is withdrawn withinmember 110, increasing the area F1 (or F2), as shown in full lines inFIGURE 6, until the open ends of both 11) and 112 are in the same plane,at which point the cross-sectional discharge area (F1 or F2) of member11@ is a maximum. Conversely, when bell crank lever 12@ moves rack 11Sto the right, choke pipe 112 is moved to the left which progressivelyreduces the crosssectional area of the passageway between its outer walland the inner wall of conduit portion 101, until choke pipe 112 contactsVtapered portion 111, as shown in dotted lines in FGURE 6, whereupon thetotal crosssectional area (F1 or F2) of member 110 is reduced to thecross-sectional area of the end of choke pipe 112.

Since the propelling thrust of a jet motor is a function of thecross-sectional area of the jet of exhaust gases, the thrust of theengine may be varied and controlled by regulating the cross-sectionalarea (F2) of the tailpipe through which the exhaust gases aredischarged, as indicated above. Also, since the thrust of a jet engineis a function ot the mass air ow through the engine, the thrust ot theengine may be Varied and controlled by regulating the cross-sectionalarea (F1) of the air intake duct of the engine. This may be accomplishedin the same manner as just described for regulating the cross-sectionalarea (F2) of the tailpipe, by applying the same control mechanism to theair intake duct instead of the tailpipe. Irrespective of whichapplication of this control mechanism is used, the fuel supply to theengine is regulated by bellows 121-on the mass air or gas iiow throughthe engine, so as to maintain a proper mixture under all operatingconditions.

As shown in FIGURE 8, bellows 121 is housed in an air-tight chamber 123,with its upper end fixed to the top wall of said chamber, and its lower,movable end attached by a rod 124 to the regulating arm 62 of fuel pump63. The interior o1 bellows 121 may be connected by a conduit 125 toPitot tube 8, and the interior of chamber 123 (outside of bellows 121)may be connected by a conduit 126 to conduit 9 (FiGURE l); so that thepressure inside bellows 121 is the same as the total pressure (P1) atair inlet 2, and the pressure inside chamber 123 is the same as thestatic pressure (Pb) at air inlet 2. The downward force exerted bybellows 121 on arm 62 is thus proportional to the difference between thetotal and static pressures at air inlet 2 which, as shown hereinabove,is a measure of the air flow through the engine 1. This downward forceof bellows 121 is opposed by a constant rate spring 127 which acts tomove arm 62 upwardly, upon a decrease in the pressure dierential actingon bellows 121. With the foregoing arrangement, it is clear that whenthe flow of air through the engine increased, the pressure diterentialacting on bellows 121 increases proportionally, and by moving arm 62downwardly (in a counter-clockwise direction), the fuel liow iscorrespondingly increased, and vice versa, so that the mixture ratio ismaintained at the desired value.

Alternatively, the fuel flow may be similarly regulated by the iow ofexhaust gases from outlet '7, by connecting conduit 125 to Pitot tube11) (FIGURE 1), and connecting conduit 126 to conduit 11; so that thepressure inside bellows 121 is the same as the total pressure (P2) oftherexhanst gases at outlet 7, and the pressureY inside ''chamber 123 isthe same as the static pressure (Pd) at outlet/7.

Operation of control system The operation of the control system is basedupon the following principles:

(1) The jet thrust developed by a jet engine is propor- 'tional to themass air ow through the engine which is a function of the differencebetween the velocity heads at the air inlet and exhaust gas outlet ofthe engine, the

lair inlet and exhaust gas outlet, Vmodified Vby the ratio between theareas of the inlet and outlet, and compensated for the variation in thedensityV of the exhaust gases with Variations in their temperature andpressure and the Valtitude of flight (atmospheric density), is a measureof the jet thrust of the engine.

(4) A forceproportional (3) is applied to one end of a servo valve 29which is subjected at its other end to a force determined by thepositioning of a manual control lever.

(5) Any inequality between the two forces acting on the servo valveactuates the valve and Vits movement varies the rate Yof output of thefuel pump 63 supplying to the engine.

(6) The balancing of forces on the servo valve keeps vthe engineoperating with a jet thrust as called for by the setting of the pilotscontrol lever.

(7) The servo valves in the control mechanisms of all the engines of thegroup propelling a multi-engines aircraft are intreconncted by anhydraulic pressure line which equalizes the pressures on all the servovalves, and `thus keeps all the engines operating with an equal jetthrust.

(8) The performance of each engine is controlled from a single manualcontrol for the whole group, but each engine operates independently ofall the others insofar as any correction required to bring its thrust inbalance vwith the thrusts of the other engines is applied to that engineonly. The single manual control may be common to all the engines and notpertain to any one of them l (as in FIGURE 1) or the manual control ofone of the engines may be selected as the single control Vfor the group(as in FIGURE 2).

(9) The control mechanism of each engine includes an automatic overridemaximum temperature and/or ,speed control which prevents overheatingand/or overspeeding of that engine, without affecting the operation ,ofthe other engines.

More specifically, the operation of my control system is as follows:

i- Each engine is provided with Pitot tubes 8 and 10 forY respectivelymeasuring the total pneumatic pressures .ppof theY air. entering airinlet 2 and p2 of the exhaust gasesvdischarged through outlet 7. Means(conduits 9 and 11) are provided for taking off the static pressures ofthe air pb at inlet 2 and of exhaust gases pd at outlet 7.

Pressures pa and pb act on opposite sides of diaphragm 13 in chamber 12,producing a thrust on rod 16 of pa-pb=h1, while pressures pc and pd actsimilarly on diaphragm .15 in chamber 14, producing a thrust on rod 18of pc-pd=h2. Rods 16 and 18, connected to link -20 on opposite sides ofits pivot 21, tend to rotate the link in opposite directions, thereforethe thrust of rod 416is subtractive from the thrust on rod 18, and in aratio which varies Ywith the position of pivot 21 from its mid-position,as shown in FIGURES l. and 2, to its lowest position near the point ofattachment of rodV 18 to link 26. Pivot 21 is shifted by rack 23 andVpinion 26 and the latter is connected to the mechanism which varies thecross-sectional area F2 of outlet 7 as Vdescribed hereinabove. As theareas of diaphragme 13 and "15 are equal and proportional tothecross-sectional area F1 of air inlet 2, the net thrust (to the right) onrod 18 is proportional to F1 (h2-h1).

Compensating device 30-40, modifies the thrust transmitted from rod 18to rod 28 through link 27, by shifting pivot sleeve 30 of link 27 inproportion to variations in the density 'y2 of the exhaust gasesdischarged through outlet 7, so that the thrust on rod 28 isproportional to 2F172(h2h1) which is proportional to the jet thrust ofthe engine, as shown by Equation 6 above.

The thrust ot rod 28 on servo valve 29 is opposed by the force of piston67, transmitted through spring 68.

Piston 67 is forced to the right by the oil pressure in the vconnectedby conduits S2Y and 53, the oil pressure in cylinder Sti is equal tothat in the left end of cylinder 42.

If the thrust on rod 72, as determined by the setting of manual controllever 80, is'made greater than that of vthe oil pressure in cylinder 50,servo valve 51 will move to the right from its neutral position, asshown in FIG- URES 1 and 2, and oil under higher pressure from pump VY45will be admitted to cylinder 50 (and also to the left end of cylinder42) and servo valve 51 will move to the left until the oil pressure incylinder 50 again equals the thrust on rod 72, when servo valve 51 willremain in its neutral position, until the balance between the thrusts onrod 72 and the oil pressure in cylinder 50 is again disturbed, either bya new thrust on rod 72 from a new position of manual control lever 8),or a change occurs in the oil pressure in cylinder 50 from a movement ofpiston 67 in cylinder 42. Conversely, if the oil pressure in cylinder 50(and the lett end of cylinder 42) increases above that necessary tobalance the thrust on rod 72, servo valve 51 will move to the left thusopening communication between cylinder 50 and drain pipe 49. VThispermits oil to escape back to tank 46 and lowers the pressure incylinder 50 until it reaches a value equal to the thrust on rod 78 whenservo valve will return to its neutral position and remain there untilthe. balance of forces on servo valve 51 is again disturbed.

Similarly, the position of servo valve 29 is determined by the balancebetween the thrust on stem 28 and the oil pressure in the left end ofcylinder 42 transmitted through piston 67 and spring 68. As long asthese forces are in balance, servo valve 29 will remain in its neutralposition, as shown in FIGURES 1 and 2. If, for any reason the jet thrustof engine l should increase, the thrust to the left on stern 28 will becorrespondingly increased, overcoming the force of spring 68, and servovalve 29 will move to the left and uncover the entrance of conduit 4S.This permits oil to escape from cylinder 55 of motor 56, throughconduits 54 and 48, back to tank 45. This lowers the oil pressure incylinder 5S and permits spring 64 to force piston 57 down which reducesthe rate of delivery of fuel oil from pump 63 to the burners 4 incombustion chamber 3, and thereby reduces the jet thrust of the engine,until the correspondingly reduced thrust on stem 28 is less than theforce of spring 68, whereuponV servo valve 29 will again move to theright until it reaches its neutral position and equilibrium is restored.Conversely, if the oil pressure in the left end of cylinder 42 isincreased by a movement of servo valve 51, responsive to a clock-wisemovement of manual control lever 80, as described above, 'piston 67moves to the right, increasing the compression of spring 68, whichovercomes the thrust on stem Z8, and servo valve 2.9 moves to the right.This movement uncovers conduit 43 and permits oil under higher pressurefrom pump 45 to flow through conduit 54 into cylinder 55 of motor 56,where it overcomes the force of spring 64 and moves piston 57 up,increasing the rate of fuel delivery of pump 63 to the burners 4 andthereby the jet thrust of the engine. The increased thrust of the enginecorrespondingly creases the thrust to the left on stern 28 until itovercomes the force of spring 68, whereupon servo valve 29 moves to theleft until it reaches its neutral position and equilibrium is againestablished.

From the foregoing, it is clear that the engine l will at all timesdevelop a jet thrust which is responsive to, and determined by, theposition of the manual control lever Si?, and with lever 80 in aselected position, any variation in the jet thrust of engine l will beautomatically corrected by the action of servo valve 29 on fuel pump 63,so as to maintain the jet thrust of the engine at a constant value, asdetermined by the setting of manual control lever 8G.

It is further apparent that action of servo valve 29 is at all timescontrolled by the action of servo valve 51 which determines the oilpressure in conduit 69 andisince conduit 69 is connected through branchconduits S6 with all the other engines, servo valve 51 will equallycontrol all the engines through their individual servo valve 29.Moreover, since the oil pressure in the left end of cylinder 42 on eachengine is equalized by interconnecting oil conduit 69, the jet thrustsof all the engines will be equalized and responsive to the action ofservo valve 51 which is controlled by the common manual control leverS0. Furthermore, since each individual engine is automaticallycontrolled by its servo valve 29, any variation in thrust of one enginewill be eliminated by the operation of its own servo valve 29 Withoutaffecting the operation of the other engines.

The above description of the operation of my control system has beenbased upon the arrangement shown in FIGURE l. However, the operation ofthe arrangement shown in FIGURE 2 is substantially the same, when themanual control lever 80 of one of the engines has been selected as thecontrol for the group of engines and the other manual control levers arerendered inoperative by locking the lower ends of levers 71 of the otherengines by means of their cam latches SS which are rotated 90 to theleft so as to hold in fixed position the plates contacting the lowerends of said levers (see FIGURE 4).

The above description of the operation of my control system has beenpremised upon controlling the operation of each engine by varying itsfuel supply. However, my control system is not limited to thisparticular method of control, but is equally applicable to controllingthe operation of each engine by either varying its air supply or byVarying the discharge of its exhaust gases.

If the air supply to the engine is the selected medium of control, thearea F2 of the exhaust gas outlet 7 is fixed (constant) and themechanism for varying the crosssectional area F1 of the air inlet 2 isconnected to link 61, and the arm 62 of fuel pump 63 is disconnectedfrom links 61. The fuel pump 63 is then regulated by a fuel controlmechanism responsive to the pressure P1 at the air inlet 2. In thiscase, the pinion 26 operating the rack 23 is connected to the mechanismfor varying the area F1 of air inlet 2, instead of being connected to amanually operated means (control lever 80) for varying the area F1.

Similarly, if the discharge of exhaust gases from the engine is theselected medium of control, the area F1 of the air intake 2 is'txed(constant) and the mechanism for varying the cross-sectional area F2 ofthe outlet 7 is connected to the link 61, and the arm 62 of fuel pump 63is disconnected from link 61. The fuel pump 63 is then regulated by afuel control mechanism responsive l4 to the pressure P2 at outlet 7 (seeFIGURE 8). In this case also, the pinion 26 operating rack 23 isconnected to the mechanism for varying the cross-sectional area F2 ofthe exhaust gas outlet 7, instead of being connected to a manuallyoperated means (control lever for varying the area F2.

While I have shown and described the preferred embodiment of myinvention, I do not limit my invention to the constructional detailsdisclosed by way of illustration, as these may be changed and modifiedby those skilled in the art without departing from the spirit of myinvention nor exceeding the scope of the appended claims.

I claim:

1. In an aircraft propelled by a jet engine having an air inlet, and anexhaust gas outlet, a fuel supply apparatus for controlling the speed ofight by the jet thrust of the engine, comprising: manually movablecontrol means for creating and ymaintaining a control force which variesin accordance with the movement of said control means; means formeasuring the unit impact and static pressures 'at said inlet andoutlet, irst means, responsive to the differential between the saidinlet unit impact and static pressures, for creating a rst forceproportional to said differential; second means, responsive to thedifferential between said outlet unit impact and static pressures, forcreating and maintaining a second force proportional to said lastmentioned differential; said iirst and second forces being proportionalto the velocity pressures at said inlet and outlet, respectively; thirdmeans, responsive to the difference between said rst and second forces,for creating and maintaining a regulating force which is proportional tosaid difference and is opposed to said control force; and fourth means,responsive to the resultant of said control and regulating forces, forregulating said jet thrust in accordance with said last-mentionedresultant force, whereby said jet thrust is varied in proportion to themovement of said control means, and said speed is controlled inaccordance with the magnitude of said jet thrust.

2. Control apparatus according to claim l, wherein said fourth meanscomprises means for varying said fuel supply in accordance with saidlast-mentioned resultant force.

3. Control apparatus according to claim 1, wherein said fourth meanscomprises means for varying the crosssectional area of said air inlet inaccordance with said last-mentioned resultant force.

4. Control apparatus according to claim l, wherein said fourth meanscomprises means for varying the crosssectional area of said exhaust gasoutlet in accordance with said last-mentioned resultant force.

5. Control apparatus according to claim l, wherein said fourth meanscomprises means for simultaneously and coordinately varying said fuelsupply and 4the crosssectional area of said air inlet, in accordancewith said last-mentioned resultant force.

6. Control apparatus according to claim l, having fifth means, formeasuring the density of the exhaust gases at said exhaust gas outlet,and for modifying said regulating force in accordance with said density.

7. Control apparatus according to claim 6, wherein said fourth meanscomprises means for varying said fuel supply in accordance with saidlast-mentioned resultant force.

8. Control apparatus according to claim 6, wherein said fourth meanscomprises means for varying the crosssectional area of said air inlet inaccordance with said last-mentioned resultant force.

9. Control apparatus according to claim 6, wherein said fourth meanscomprises means for varying the crosssectional area of said exhaust gasoutlet in accordance with said last-mentioned resultant force.

10. Control apparatus according to claim 6, wherein said fourth meanscomprises means for simultaneously and coordinately varying said fuelsupply and the cross- Vsectional area of said exhaust gas outlet, inaccordance with said last-mentioned resultant force.

11. Control apparatus according to claim 6, having means for controllingthe speed and temperature of said engine so that neither exceeds aselected safe value.

12. Control apparatus according to claim 7, having means for controllingthe speed and temperature of said engine so that neither exceeds aselected safe value.

i References Cited in the le of this patent UNITED STATES VPAUEIITS2,306,953 Jung Dee. 29, 1942 2,404,428 Bradbury July 23, 1945 2,457,595Orr Dec. 28, 1948 2,466,908 Perrill Aug. 12, 1949 2,537,772 Lundquist etal. Jan. 9, 1951 2,540,594 Price Feb. V6, 1951 OTHER REFERENCES AeroDigest Gas Turbine Propulsion Systems, by A. H. Redding, May 1947, pages75-77 and 149. 15 Jet Propulsion and Gas Turbines by M. I. Zucrow; JohnWiley and Sons, New York, 1948, pp. S14-516.

Gas Turbines For Aircraft by F. W. Godsey, Jr. and L. A. Young;McGraw-Hill, 1949; pp. 193195, 233.

